netdev - Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe)

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Message-Id: <20090430.070811.260649067.davem@davemloft.net>
Date:	Thu, 30 Apr 2009 07:08:11 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	andrew@...dna.net
Cc:	jelaas@...il.com, netdev@...r.kernel.org
Subject: Re: tx queue hashing hot-spots and poor performance (multiq, ixgbe)

From: Andrew Dickinson <andrew@...dna.net>
Date: Thu, 30 Apr 2009 07:04:33 -0700

>  I'll do some debugging around skb_tx_hash() and see if I can make
> sense of it.  I'll let you know what I find.  My hypothesis is that
> skb_record_rx_queue() isn't being called, but I should dig into it
> before I start making claims. ;-P

That's one possibility.

Another is that the hashing isn't working out.  One way to
play with that is to simply replace the:

		hash = skb_get_rx_queue(skb);

in skb_tx_hash() with something like:

		return skb_get_rx_queue(skb) % dev->real_num_tx_queues;

and see if that improves the situation.
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